As disclosed in U.S. Pat. No. 3,879,243, in the construction of water wells or waste wells, a pipe construction having a porous wall is normally used. The porous wall may be thought of as a screen which permits water to flow through the wall and which keeps sand and granular material out of the well. Wells must be developed in whatever soil is available and there is no control over the grain size of the soil that is adjacent the wall of the pipe or screen. Thus, it is necessary to use a very fine mesh screen having openings for example in the order of 0.006 inch. Even where such a small size screen is used, grain material that is smaller than the mesh will pass therethrough and harm both the flow of the well and equipment in the well.
In order to avoid the excesive costs of wire screening, it is known to cut slots, such as by sawing in the wall of a pipe. However, the wall is weakened as a result of the quantity of material that is removed. When glass fibres are used in the pipe, the slotting technique has an additional detrimental effect in that individual strands of the pipe that are wound continuously are cut so that, even in areas where material is not removed, the pipe is weakened.
A further method used in well preparation is the digging of a hole larger than the outside diameter of the pipe to be inserted therein, and packing gravel in the annular opening that is formed in order to insure that fine material is trapped in the gravel. Normally, the gravel consists of granules that are large enough not to enter the openings in the screen. Drawbacks to the gravel packing technique are that the gravel must frequently be shipped over large distances and excessive costs are incurred in packing the gravel into wells. Also, unless the gravel packing is done absolutely perfectly, there is always the possibility of collapse due to the weight of the gravel.
U.S. Pat. No. 3,601,159 discloses a porous tube, the wall of which consists of the combination of a porous paper strip and a layer of resin-impregnated glass fibres. The paper strip may be on the outside or the inside diameter of the pipe. In both embodiments the glass fibre rovings are furnished with just enough resin (i.e., resin starved) to hold the glass together without filling the interstices between rovings so that the resulting structure will be sufficiently permeable to allow the flow of water therethrough.
U.S. Pat. No. 3,879,243 provides a pipe having a porous, monolithic wall. Layers of resin bonded glass fibres are wound in a helical pattern on a mandrel together with a matrix material that is removable by application of heat, a solvent or a vacuum. After the resin is cured, appropriate means are used for the removal of the matrix material. The resulting structure is a pipe having a wall whose porosity is determined by the volume of the matrix material that is initially applied and subsequently removed.
Various other techniques have been tried which utilize resin bonded glass fibres but the use of resin starved glass fibres has been found essential to prevent blockage by the resin of the openings through which water is to pass. The use of resulting pipes, as well as of cement asbestos pipes which they have been intended to replace, has led to the occurrence of failure in deep wells where pressures may exceed, for example, 600 p.s.i. which is strong enough to make known types of pipes, otherwise suitable for this purpose, collapse.